Pencil sheath compositions

ABSTRACT

Pencils made with a resin-based sheath to replace wood sheaths. A sheath material consisting essentially of a resin binder, a fibrous filler and a metallic soap is extruded around a marking core. The resulting extrudate is immediately chilled after leaving the die, and cut into pencil lengths. The apparatus includes core feeding and transport means, core preheating means and chilling means. The resulting pencils possess the physical qualities associated with wood-sheathed pencils due to the fine, closed cell structure of the sheath material. The surface of the sheath is smooth and may be coated with a pigmented resin or painted.

U Umted States Patent 11 1 1111 3,875,088

Arons et al. 1 1 Apr. 1, 1975 [54] PENCIL SHEATI-I COMPOSITIONS3,033,695 5/1962 Glab 106/163 5] n entors: r ing J. Arm's, eabody; obert3,704,071 11/1972 Muller et a1. 401/96 n Boston; Richard M -i FOREIGNPATENTS OR APPLICATIONS Wakefield, all of Mass. 2,055,894 4/1971 France401/96 [73] Assignee: Hasbro Industries, Inc., Pawtucket, OTHER PUBLIRose et al., The Condensed Chemical Dictionary, Seventh Edition, VanNostrand Reinhold Co., N.Y.C., [22] F1led. Apr. 6, I973 966 pp 42 and852. [21] Appl. N0.: 348,664

Primar Examiner-Allan Lieberman Related US. Application Data y [63]Continuation-impart of Ser. N0. 163,303, July 16. Attorney Agem orFrmTShaPIm and Shap'm 1971, abandoned. ABSTRACT 52 us. c1 260/25 11,106/155, 106/158, Penci's made with resin-based Sheath replace M1163106/17], 106/194 260/8, 26OH74 wood sheaths. A sheath materialconsisting essentially R, 260/18 R 401/96 ofa resin binder, a fibrousfiller and a metallic soap is [51] Int CL 843k 19/14, Cogf 47/10, Cosh17/18 extruded around a marking core. The resulting extrud- [58] Fieldof Search 260/17 4 R 17 4 BB 17 4 CL ate is immediately chilled afterleaving the die, and cut 260/2 1'06/17l 163 into pencil lengths. Theapparatus includes core feed- 1 2 601 5 i 6 ing and transport means,core preheating means and chilling means. The resulting pencils possessthe physi [56] References Cited cal qualities associated withwoodsheathed pencils UNITED STATES PATENTS due to the fine, closed cellstructure of the sheath ma- 1 937 104 11/1933 Thomsen 401/96 ierial- TheSurface the sheath is and may be 2:855:320 10/1958 Gabriel 106/163Coated with a Pigmented resin Or P 2,976,164 3/1961 Glab 106/1632,988,764 6/1961 Lorenian 401 96 Clams 18 Drawmg IE; IIiII AIR I E13 5BINDER FIBROUS FILLER COMPOUNDING GRANULATING METALLIC SOAP ADJ USTINGMOISTURE CONTENT CHILLING EXTRU DING CROSS HEAD COOLING CUTTING PENCILSCORE AND DIE SSEMBLY EXTRUDING COATING RESIN F'IEJ PREHEATING mVENTORSIRV\NG J. ARoNs ROBE-RT ELLE INVENTORS IRVHJQ J. ARDMS Rosana ELLER cuCHAR 72am u. a afw A'T QRME.

0 f on-..

INVENTORS \RVHJG J.AROM5 ROBERT ELLER BY FMCHARD ELMERRHA.

ATTORNEY PENCIL SHEATH COMPOSITIONS The invention relates to pencilmanufacture, and is more particularly directed to the manufacture ofpencils having an extruded, synthetic resin-based sheath.

This application is a continuation-in-part of our pending applicationSer. No. 163,303, filed July l6, I97 I now abandoned.

BACKGROUND OF THE INVENTION Pencils are normally formed by enclosing themarking core in wooden sheaths. The wood used must meet certain physicalstandards of strength, dimensional stability and sharpenability. Thepresent commercial pro cess for making pencils is a multistep one, timeconsuming and relatively expensive. Substitutes for the wooden sheathsas well as for the involved manufacturing process have long been sought.It is, however, difficult to form a sheath material which issatisfactory bonded to the marking core, and which the user will acceptas a substitute for the well-known wood sheath. This is due to the factthat the sheath must meet certain desired criteria includingsharpenability, adequate stiffness, good flexural or breaking strength,relatively low density and bondability to the marking core.

Many attempts have been made to manufacture pencil sheaths from amaterial other than wood. It has been proposed to manufacture pencilsheaths by extrusion and subsequent drying of an aqueous pulp of wood orpaper with a suitable hinder, or to tightly wrap the marking core withpaper and the like. in the first instance, such attempts have beenunsuccessful because the necessity of expelling large amounts of waterfrom the extrudate gives rise to warped pencils and loose cores. Wherepencils have been made by wrapping the core, problems have arisen inadhering the wrapping material to the core, as well as adhering thelayers of wrapping material to each other, and in producing a straight,properly aligned sheath that could be readily sharpened by a penknife ormechanical sharpening device.

US. Pat. Nos. 2,988,784 and 2,790,202 disclose a sheath composition, amethod, and an apparatus for extruding a sheath around a marking core tomake a socalled scissible writing instrument. The sheath compositiondisclosed is a mixture of a main ingredient (wood flour and the like), awaxy substance such as chlorinated naphthalene, a thermoplastic bindersuch as polyvinyl chloride, a plasticizer for the binder, and alubricant. The sheath composition is blended and used in a completelydry condition, this being the patentees way of avoiding the difficultiesencountered in the prior art compositions and methods.

In the method and apparatus of US. Pat. No. 2,790,202, techniques andmeans are used to extrude the sheath around leads fed along avertically-oriented axis. Cooling of the sheath is accomplished beforethe sheathed lead leaves the die nozzle.

The composition, method and apparatus of US. Pat. No. 2,988,784 and2,790,202 present certain inherent difficulties and limitations. Amongsuch difficulties are the need for working with completely dry sheathmaterial, the need for using an adhesive to bond the core to the sheath,and the necessity to accurately control the radial component of pressurein relation to the axial component of pressure on the sheath material toovercome the back pressure in the die brought about through the verticalfeeding of abutting core lengths. To the best of applicants knowledge,this prior art teaching which overcomes some of the disadvantages andlimitations of the art preceding it has a number of limitations of itsown, which have apparently prevented it from achieving any commercialsuccess.

SUMMARY OF THE INVENTION It is an object of this invention to provide anovel and improved composition which can be extruded around a markingcore to form the sheath of a pencil. It is another object to provide acomposition which may be extruded at temperatures lower than usuallyemployed, and which is directly bondable to the marking core, therebyeliminating the need for an adhesive. It is still another object toprovide such a sheath composition which when extruded and cooled is madeup of fine cells imparting to the sheath good sharpenability and asmooth, denser outer surface which readily lends itself to theapplication of a colored coating.

It is another object of the invention to provide an improved pencil thesheath of which is formed of a thermoplastic material and possesses thecharacteristics of sharpenability, adequate stiffness, adequate flexuralor breaking strength, low density, and bondability to the marking coreassociated with wood-sheathed pencils.

It is a further object of this invention to provide an improved methodof forming pencils in the form of a thermoplastic sheath extruded aroundand directly bonded to a marking core. It is another object to provide amethod of the character described which is continuous in operation andproduces pencils having the physical characteristics of wood-sheathedpencils.

It is still another object to provide improved apparatus for using thecomposition of the invention, and to carry out the'met-hod of theinvention to produce improved thermoplastic resin sheathed pencils.

The composition of the invention which is extruded around the markingcore to form the sheath of the pencil consists essentially of, byweight, approximately 50 to 757: of a thermoplastic resin binder,approximately 20 to 4071 of a fibrous filler, and approximately 0.5 tol5)? of a metallic soap. The ratio of binder to fibrous filler isapproximately L5 to 3.0. To furnish the desired fine, closed cellstructure for the sheath, the composition contains 0.3 to 2%, by weight,of moisture. Preferably, the moisture content is 0.8 to 1%.

By the method of the invention, pencils are made by formulating thesheath composition material, controlling the moisture content thereof,extruding it hot onto marking cores which are preheated to facilitatebonding to the sheath material, and then rapidly chilling the resultingextrudate comprising the marking core axially aligned within the sheath.After a final cooling, the extrudate is cut into the desired pencillengths. Subsequent to the formation of the sheath around the core butprior to the withdrawal of the extrudate from the die, the sheathsurface may be, and preferably is, coated with a pigmented thermoplasticcoating by extruding a coating composition onto it. Alternatively, theextrudate may be painted in the same manner as wood-sheathed pencils.

The apparatus of this invention comprises a crosshead and die assemblyadapted to extrude a softened or fused resin-based material around amarking core, means to feed the core material, in the form of abuttinglengths, into the crosshead and die assembly, means to preheat the corelengths prior to their introduction into the crosshead and die assembly,means to provide the sheath forming material as a fused resin'basedmaterial into the crosshead and die assembly, means to rapidly chill theextrudate sheath containing the core and then to further cool it, andmeans to withdraw the extrudate from the die. Means may also be providedfor extruding a resin coating over the extruded sheath before the extrudate leaves the die, and to cut the extrudate into predeterminedlengths.

The resulting pencil is characterized by good sharpenability, accuratealignment of the core within the sheath and tightly bonded thereto, asmooth pleasing surface, and completely adequate strength. Examinationof the sheath material shows it to be in the form of fine, closed,uniformly sized cells, believed to be the result of a small, butcritical amount of moisture present in the sheath forming material priorto extrusion. The size of these fine closed cells decreases radiallyfrom the core out to the pencils surface, producing a concomitantincrease in density radially outward to provide a smooth exteriorsurface. It may be postulated that this in turn is due to the rapidchilling of the extrudate after it leaves the die nozzle.

These, and other objects and advantages of the invention will beapparent from the following detailed description taken in conjunctionwith the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a flow diagram showing thesteps in compounding the sheath material and in the formation of apencil using the sheath material;

FIG. 2 is a simplified, top plan view of apparatus suitable forprocessing a sheath composition in accordance with the invention, thisview further indicating an exemplary set of temperatures for one sheathcomposition at various zones of the apparatus;

FIG. 3 is a side elevation, partly cut away, of the marking core feedingmechanism;

FIG. 4 is a vertical cross section taken approximately in the plane ofline 4--4 of FIG. 3;

FIG. 5 is a top plan view of the core transport system;

FIG. 6 is a vertical cross section taken approximately in the plane ofline 6-6 of FIG. 5;

FIG. 7 is a side elevation, partly cut away and in cross section, of thecore preheater;

FIG. 8 is a vertical cross section of one embodiment of a crosshead anddie assembly and its relationship with the core preheater;

FIG. 9 is a cross section taken approximately in the plane of line 9-9of FIG. 8;

FIG. 10 is a cross section of another embodiment of a portion of the dieshowing a hexagonal-shaped die as an alternative to the circular die ofFIG. 9;

FIG. II is a cross section taken approximately in the plane of line Il1lof FIG. 10.

FIG. 12 is a vertical cross section of another embodiment of thecrosshead and die assembly which includes means to apply a coating tothe outside surface of the sheath;

FIG. 13 is a side elevation, partly cut away and in cross section, ofthe chilling means;

FIG. 14 is a cross section taken approximately in the planes of linesl414 of FIG. 13;

FIG. 15 is a perspective view, partly in cross section, of the coolingmeans;

FIG. I6 is a view of the pulling means;

FIG. 17 illustrates a pencil made in accordance with this invention; and

FIG. I8 is an enlarged cross section of the pencil shown in FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now bedescribed in greater detail with regard to the composition andformulation of the sheath material, the method of using the sheathmaterial to form pencils, the apparatus used to carry out the method,and the resulting article of manufacture.

Composition of the Sheath Material The sheath material consistsessentially of a thermoplastic resin binder, a fibrous filler and ametallic soap. Each of these essential components is believed to serveseveral purposes in creating a good sheath.

The thermoplastic resin functions as a binder for the filler, to enhancethe extrudability of the sheath at relatively low temperatures, and tocontribute to the ease of fabrication to give a sharpcnable,low-stretch, substantially rigid sheath.

Since no adhesive need be used, The resin binder is capable of providinga suitable bond to the marking core; and also preferably, the sheath iscapable of providing a base for the bonding thereto of a coatingmaterial. Thermoplastic, extrudable grade resins suitable as a componentof the sheath material include, but are not limited to,styrene-acrylonitrile resins, acrylonitrilebutadiene-styrene resins,rubber-modified impact polystyrene resins, ethyl cellulose and thecellulose ester resins (e.g., cellulose acetate, cellulose butyrate andcellulose propionate), homopolymers and copolymers of the vinyl resinsand the like. A preferred thermoplas tic resin is anacrylonitrile-butadiene-styrene resin having a Vicat softening point of212F and a specific gravity of L05. In general, the Vicat softeningpoint of the resin is preferably above about I80F.

The amount of the thermoplastic resin binder may range betweenapproximately 50 and 75% by composition weight, with approximately 65 topreferred.

The fibrous filler performs the multiple functions of serving as areinforcing filler to increase rigidity and flexural strength, enhancingthe sharpenability of the final pencil, and as the source of themoisture required in the formation of the fine cellular structureattained and responsible for the good sharpenability and low density.

Suitable fillers are preferably cellulosic in nature, but such tillersas micronized leather may also be used. Cellulosic fillers which may beused include, but are not limited to, such comminuted materials assoftwood flour, cotton linters, chopped or hammermilled rayons, hardwoodflours, walnut shell flour, peanut shell flour, pecan shell flour, sisalfibers, cotton flock, wood pulp and mixtures thereof. A preferred fillermaterial is a softwood flour sized such that 96 to 98% passes through alOO-mesh screen, e.g., of a particle size of about I50 microns and less.Wood flours between 200 and 40-mesh size, e.g., between about and 425microns may be used. The filler should be present in an amount rangingbetween approximately 20 to 40%, by weight, of the sheath composition.

The metallic soap functions as an extrusion aid to permit the use oflower than normal extrusion temperatures and acts as a lubricant to aidsharpenability It appears to also contribute to the attainment ofuniformity of cell formation and to the resulting desired cell structurein general.

The term metallic soap" is used herein in the sense defined on pp. 195,vol. 5, I950 edition and 573, vol. 12, l954 edition of the Kirk-OthmerEncyclopedia of Chemical Technology. Metallic soaps contain a metalother than sodium or potassium, and are for the most part alkaline earthor heavy-metal salts of monobasic carboxylic acids of the generalformula (RCOO),M, where M is a metal radical of valence state .r and Ris an organic radical containing at least 67 carbon atoms. Whilemetallic soaps are insoluble in water, the term as herein used includeslithium salts which are moderately soluble, Examples of metallic soapswhich are preferred are the stearates, oleates, palmitates,ricinoleates, and laurates of calcium, aluminum (mono-, di-, and tri-),magnesium, zinc, and lithium. Such metallic soaps are preferred becauseof their non-toxicity.

A preferred metallic soap is a micronized aluminum stearate having amelting point of between l50 and 155C (about 300F) and sized such thatabout 95% passes through a ZOO-mesh screen, e.g., of a particle size ofabout 75 microns or less. For uniform distribution, the metallic soappreferably is used in the form of 25 a fine particulate material, and itmust have a softening point below the temperature at which the sheathcomposition is extruded around the core.

The metallic soap is present in the sheath composition in a rangebetween about 0.5 and about l.5%, by weight, with a preferred rangebeing between about 3 and I07: by weight.

To achieve the aforementioned desired criteria of sharpenability,adequate stiffness, good flexural or breaking strength and bondabilityto the marking core coupled with the essential ability to extrude thecomposition about the core, the binder and fibrous filler must bepresent in the binder/filler ratio of 1.5 to 3.0. To extrudc acomposition having a binder/filler ratio of 1.5, it is desirable to usean amount of metallic soap at the higher end of the range indicatedabove, or approximately I57? by weight of the composition. It ispreferred however, that the composition contain a binder/- filler ratiowhich is on the high side of the range, or approximately 2.8. Such acomposition provides a higher output rate, improved breaking strengthand a superior surface finish.

Though not essential, it is within the scope of the invention to addother ingredients including coloring material in the form of dyes orpigments, scenting agents such as those giving an odor of cedar, and thelike. These additional components are generally present in relativelysmall amounts, and are chosen to contribute any desired aestheticqualities to the finished pencil.

A significant aspect of this invention is that the sheath has a fine,controlled size, closed-cell structure. In the normal extrusion ofthermoplastic resins, it has always been considered essential to utilizea dry resin compound to avoid cell formation and to eliminate largeclosed voids in the extruded product. it has been found, however,contrary to this past practice, that if a small, but controlled amountof moisture is present in the sheath material as it is introduced intothe extruder, it is possible to utilize the moisture for the formationof the desired cellular structure in the finished extruded sheath. Theamount of moisture in the sheath composition is in the range of betweenabout 0.3 and about 2%,

by weight, with the preferred range being between about 0.8 and 1%. Bycontrolling the moisture content of the sheath composition within thisfairly narrow range and by using relatively low extrusion temperaturesand high extrusion pressures, it is possible to control the cell sizeand distribution within the desired ranges.

Where the conditions are such that it is difficult to control thehumidity conditions, or to allow less rigid control of moisture, a smallamount of a blowing agent may be included in the sheath composition.Examples of suitable blowing agents which may be used areazodicarbonamide, l,l -azobisformamide, p, p -oxybis (benzene sulfonylsemicarbazide), dinitrosopenta methylene tetramine, bis-benzenesulfonylhydrazide, asobisisobutyronitrile, and sodium bicarbonate. The blowingagent may be present in the amount of 0 to 2.0%, the preferred rangebeing 0.05 to 1.07: by weight of the total composition. If a blowingagent is used, the moisture content may be somewhat reduced withoutadversely affecting the uniform cellular structure of the extrudedproduct.

As hereinbefore indicated, one of the functions of the metallic soap isthat it acts as an extrusion aid. If desired, a small amount of anextrusion aid in addition to the metallic soap may be included in thesheath composition; for example, polyethylene, a hydrocarbon wax, afatty acid ester, a fatty acid amide, or a fatty acid. If an addedextrusion aid is included in the composition, it may be present in theamount of 0 to 5.0%, the preferred range being in the amount of 0.5 to2.5%, by weight, of the total composition.

Since the fibrous fillers normally contain moisture (e.g., approximately6% equilibrium moisture content in wood flour) the moisture ispreferably introduced as an integral part of the filler, and thenreduced to the de sired level by heating. Alternatively to the compounding of sheath composition as a dry material, it may be mixed as a slurryand the water removed in an appropriate manner to the desired level.

In formulating the sheath composition, the fibrous filler and metallicsoap are dry blended at room temperature in conventional blendingequipment. Then this dry mixture, together with the thermoplastic binderare fed into a eoninuous-melt blender such as a Banbury or Farrellmixer. The blending temperature is maintained at a sufficiently nighlevel to melt the resin binder without thermally degrading the filler orthe resin. Subsequent to mixing and cooling, the product is granulated,brought to the desired equilibrium moisture content by adding orremoving water and then sealed in an air-tight, moisture-impermeablecontainer until used.

If desired, the resin binder may be in the form ofa latex, whereupon itis added to the fibrous filler and mixed until the filler is uniformlydistributed and thoroughly wetted out by the latex. Then the metallicsoap is added and thoroughly blended in. The resulting slurry or wetpaste is then dried in any suitable manner, such as by passing itseveral times through a two-roll mill heated to a temperature within therange specified for dry mixing to drive off excess water. This millingis continued until the composition forms a continuous band on one of thehot rolls. It is then removed and transferred to a heated blender forprocessing in the same manner as described for the relatively dryblends.

Sheath compositions were dry blended by the first described formulatingprocedure as follows:

Percent by Weight of Component Example Number Component l 2 3 4 5 h 7 8Resin Binder Acrylonitrile-hutadienestyrene resin l) 70 70 (i5 57 54 SiHigh-impact, rubber I 70 modified polystyrene (2| Fibrous Filler WoodFlourllOfi-mesh) 27 25 38 3h 34 Wood flour (40mesh) Z Metallic SoapAluminum Stcaratc ll) Sold as ABS 3l3 by Dow Chemical Company: Vic-atsoftening point I lPF, specific gravity HIS. melt flow rate 6.8 gmlltlmin; melt viscosity (i000 poiscs.

(2) Sold as Slyron 4753 by Dow Chemical Company: View softening pointItWF. specific gravity L05: melt flow rate 3.6 gnu/Ill min; melt\iscosity .1401) poiscs.

Method of Forming Pencils FIG. 1 is a flow diagram illustrating thesteps of the method of this invention. Of these steps shown in FIG. 1,at least three are believed significant. These are the controlling ofthe moisture content in the sheath composition, the preheating of thelead cores and the quick chilling of the extrudate immediately afterwithdrawal from the die.

The marking core is preheated to a temperature which approximates thatat which the sheath composition is introduced into the crosshead and dieassembly and is extruded around the core. This temperature is in turndependent upon the thermoplastic resin binder used, and is preferably atleast about lO0F above the Vicat softening point of the resin. Themarking core preferably is a lead; that is, a ceramic or vitrifiedelement made by the well-known technique of firing a mixture of clay andgraphite in the desired ratio. Since bonding of the sheath to the leadcore is achieved without the use of an adhesive, the lead core is madeso that it is free of any surface wax, the presence of which wouldinterfere with bonding.

The sheath composition with its controlled moisture content is heatedand forced under pressure through an extrudcr and caused to form asheath of a prescribed thickness around the preheated core positionedalong the axis of the sheath. The extrudate as it is withdrawn from thenozzle of the die is immediately chilled by contacting its entiresurface with expanding, compressed air which strikes the extrudatesurface in the form of a multiplicity of gas streams. These air streamsare directed into the chilling zone toward the outlet end of the chillerto form an acute angle with the extrudate surface. The extrudate duringthis chilling step is supported by the die nozzle and by a cooling meanswhich follows the chilling zone so that its entire surface is exposed tothe compressed air. Subsequent to this chilling step, the extrudate issubjected to further cooling by indirect (and if desired direct) heatexchange with a fluid coolant until it reaches substantially ambienttemperature throughout. Withdrawal of the cxtrudate from the die nozzleand through the chilling and cooling steps is accomplished by a degreeof positive pulling which may be regulated automatically to ensure auniform cross section in the extrudatc. As a final step, the extrudateis cut into predetermined pencil lengths which may then be stamped withany desired indicia and equipped with an erasure assembly as is wellknown in the pencil making art.

The cxtrudate may be coated with a pigmented coating composition bycoextruding a thermoplastic resin coating containing pigment in the formofa thin skin on it prior to its withdrawal from the die. The resincoating composition is heated above its softening point for coextrusionand is applied subsequent to the formation of the sheath. Suitableresins for coating include, but are not limited to, polystyrene,TUbbCFTfiOdlfiCd impact polystyrene resins,acrylonitrile-butadiene-styrcne resins, styrene-acrylonitrile resins,acrylic resins, polyamidc resins, cellulose-based resins, vinyl resinsand the like. The coating resin must of course be one which has aworking temperature which is within the temperature range at which thesheath is formed and be capable of forming a permanent bond with thesheath surface.

FIG. 2, which is discussed in detail below, gives exemplary processingtemperatures when using the composition of Example I as the sheathmaterial and a colored styrene resin as the coating material. it will beseen that whereas the acrylonitrile butadienc-styrene resin used as thebinder in the sheath composition is normally extruded at about 425F, thesheath material of this invention containing the relatively highpercentage of metallic soap is extruded at about 325F.

Apparatus for Forming Pencils The apparatus of this invention is shownin a simpli fied top plan view in FIG. 2. Details of the apparatuscomponents are illustrated in FIGS. 3-16. As shown in FIG. 2, thelengths of the marking core 10 are supplied to and fed from a corefeeder ll, moved along in abutting relationship by a core transportmechanism 12 into a core prehcatcr 13. The granulated sheath compositionmaterial is fed from a bin 14 into an extruder 15 through an inletadapter line 16 and into a crosshead 17. It will be appreciated by thoseskilled in the art of extruding thermoplastic materials that suitableheating means (not shown) must be provided to establish the desiredheating zones. Exemplary heaters are shown for the crosshead 17 in FIGS.8 and 12 described below. Affixed to the end of a die 18 and thermallyisolating it from chilling means 19 is a radiation shield 20, typicallyformed of a thermally insulating material such as asbestos board.Compressed air is provided to the chill means 19 through conduits 21,one of which is illustrated. The extrudate 22 is withdrawn from the die18 by means of a puller 23, passing through the chilling means 19,through a cooling means 24, which is designed to effect indirect heatexchange between the extrudate and a coolant (e.g., tap water). Thecoolant is introduced into the cooling means 24 through an inlet line 25and withdrawn through a discharge line 26. The extrudate is cut intopencil lengths 27 by a cutter 28. If the extrudate is to be coated bycoextruding a thermoplastic resin skin coating on its surface, thecoating resin is fed from supply means 29 into a coating extruder 30,through a die inlet adapter conduit 31 into the die 18. As in the caseof the sheath extrusion means, suitable heating means [not shown) areprovided for the coating extruder. If not so coated, then the cut pencillengths are coated in the same way as wood-sheathed pencils are coated.

The core feeder 11 and core transport means 12 are shown in FIGS. 3 and4. The cores are supplied in predetermined lengths and are fed into thepreheater, crosshead and die in abutting relationship to form, inessence, an endless or continuous, aligned core. The core lengths 10 arefed singly through a vertical feeding passage defined between two plates41 and 42 closed at their ends by end members such as 43 and tapered atthe delivery end. A core supply bin 44 provides the core lengths to thefeeding passage 40.

The marking core lengths 10 are moved forward out of the feeder onto anendless V-belt 45 which engages a forward pulley system 46 and an afterpulley system 47. These pulley systems are mounted on shafts 48 and 49,respectively, rotating in forward pillow blocks 50 and after pillowblocks 51. The after pulley system 47 is driven by motor 52 throughdrive pulleys 53 and 54 which are mechanically connected by belt 55. Thepillow blocks 50 and 51 and the motor support 56 are all mounted on abase plate 57.

As the cores 10 are delivered to the V-belt, they are initiallyaccurately aligned and maintained in alignment for delivery into thecrosshead. Alignment is established and maintained within the feederfirst through the alignment of belt 45 and then through alignment of thecores on the belt. As shown in FIGS. 3 and 4, alignment of the belt ismaintained by causing it to travel between two aligning strips 60 and 61affixed to a belt support plate 62. The inboard sides of these aligningstrips are bent upwardly at an angle conforming to the contour of thesides of the belt to form belt guides 63 and 64 which are spaced todefine a passage just large enough to permit the belt to travel throughthe passage with a minimum amount of friction. Alignment of the cores onthe belt is achieved through the use of core aligning strips 65 and 66,the inboard sides 67 and 68 of which are bent downwardly to form anelongated lead core passage 69 directly beneath lead core feed passage40. This elongated passage 69 is bounded on its upper side by the exitof passage 40 and on its lower side by the surface of belt 45. Thealigning strips 65 and 66 are mounted on angled support strips 70 and 71which in turn are adjustably mounted on lower angled supports 72 and 73,affixed to belt support plate 62, and to upper angled supports 74 and75. These latter, upper supports 74 and 75 in turn form the means bywhich the two plates 41 and 42 defining passage 40 are supported,through angled strips 76 and 77, above the belt. This entire supportsystem is adjustable with regard to distance from the core axis as wellas to height above the belt support plate 62.

The belt support plate 62, along with the support assembly affixed toit, is adjustably positioned above base plate 57 by means of forwardangled support plates 79 and 81 and after angled support plates 78 andwhich are apertured to permit the passage of belt 45.

As previously stated, it is necessary to advance the core lengths 10 inabutting relationship. The advancement of the cores is accomplished bymeans of a series of pusher feet 89 mounted at equally spaced intervalsalong the center line of the belt, the intervals being equivalent to thelength of the individual lead cores plus a small clearance. These pusherfeet also control the discharge of a core length onto the belt, for aslong as one of these pusher feet is traveling under the exit of passage40 in the feeder, it is'not possible for the core at the exit of passage40 to fall completely onto the belt. As soon, however, as a pusher foot89 (e.g., the one shown in FIG. 3) passes beyond the forward end of thepassage exit, the next core falls into place and a pusher foot makescontact with its after end. A positive force is required to move thecores forward to overcome the resistance provided in the crosshead asthe extruded sheath composition contacts the cores. This positive forceis provided by the pusher feet 89. The gap between consecutive corelengths is eliminated by providing the motor 52 with a slip clutchmechanism which allows the belt 45 to move faster when it is notactually pushing a core length. Thus each core length catches up withthe one ahead of it which, as explained, experiences a backward thrust.

The core transport mechanism 12 between the feeder 11 and preheater 13is shown in FIGS. 3, 5 and 6. The angled support strips 70 and 71 extendbeyond the belt 45, while the core alignment strips 65 and 66 extend tothat point where the belt contacts the pulley 46. The angled supportstrips 70 and 71, beyond the effective length of belt 45 serve tosupport a trough 90 (FIG. 6) which is aligned with belt 45 and designedto provide a passage 91 for the core 10. Passage 91 is enclosed on topby a solid metal bar 92 which is cut to fit the sides of the trough andadapted to sit in it without touching the lead cores. This bar preventsany buckling of the core lengths where they abut. The trough 90 and theentry end of the core preheater are joined by a cover plate 93 servingin the same role as the solid bar 92. At this point, the core isintroduced into the preheater.

The core preheater 13, as shown in FIGS. 7 and 8, is formed in foursections: a small diameter entry section 100, a larger diameter heatersection 101, an adapter section 102 and a threaded section 103. The topof the entry section is partially cut away to provide a flat surface 104for engagement with cover plate 93 of the core transport system. Theheater section comprises a cylindrical thermal mass of metal 105(typically formed of steel or copper) and a band resistance heater 106in thermal contact with substantially all of its surface. A thermocouplewell 107 is located in the thermal mass 105. It is, of course, withinthe scope of this invention to use other types of heaters and othertypes of temperature measuring devices if desired. A passage 108, havinga diameter slightly greater than the diameter of the core, extendsthroughout the length of the preheater.

One embodiment of the crosshead and die assembly is shown in crosssection in FIG. 8. In keeping with well known crosshead design practice,the crosshead used in this apparatus comprises a crosshead body formedof a male section 110 and a female section 111. The male section has athreaded well 112 adapted to be connected to the threaded conduitadapter 16 of the sheath material extruder (FIG. 2) to provide thenecessary communication with the annular extrusion passage 113 definedbetween the male and female sections. The fe male section is designed toprovide a circumferential ridge 114, the purpose of which is to ensureuniform distribution of the thermoplastic sheath composition material115 (FIG. 9) around and throughout passage 113. A cone 116 is attached,such as by screw means, to the preheater extending through the femalesection. The cone extends into the die 117, forming therewith a passageI18 which is a continuation of passage II3. The cone 116 has a corepassage I19 aligned with passage I08 in the prcheater. This passage I19and the conical passage I18 converge in the after end of the die at thepoint where the sheath material is extruded around and bonded to thecore forming the extrudate 22. The crosshead sections and the die,including the crosshead clamp I20, are assembled by suitable means suchas screws, as illustrated in FIG. 8. Two band resis tance heaters 121are affixed to the outer surface of crosshead l7 and another band heater112 is affixed to the outer surface of die I17. The apertured radiationshield 20 interposed between the heated die section I8 and the chillingmeans I9 is attached to the end of the die.

As shown in FIGS. 8 and 9, the extrudatc 22 (core I surrounded by sheathmaterial 115) is circular in cross section. It is also within the scopeof this invention to form the extrudate in any other desirable crosssection, e.g., hexagonal. This latter configuration is illustrated inFIGS. and II. In FIG. I0, the die opening 123 is shown without thesheath material while in FIG. II the sheath H5 is shown around the core10.

FIG. I2 illustrates another embodiment of the crosshead and dieassembly, this embodiment being adapted to coextrude a skin coatingaround the sheath. The main crosshead is the same as shown in FIG. 8.The die assembly is modified to have an additional crosshead and dieattached thereto, as by threading it onto the end ofdie II7. This secondcrosshead and die comprise a threaded adapter piece I25 which hasmachined in its face I26 a shallow circular well 127 bordered by asomewhat deeper ring 128, the well and ring forming with die block I29 aportion of the passage through which the thermoplastic resin coatingmaterial is introduced into the die. The circular well I27 is located sothat its center does not coincide with the aperture in adapter I25. thusensuring uniform distribution of the resin prior to and during itscontacting the exterior surface of the sheath. The die block I29 has athreaded well I30 which is adapted for attachment to adapter conduit 3]of the coating cxtruder 30 (FIG. 2). This well is in communication withring 128 through passage I31. The die opening in die block is sized topermit the formation of a coating I32 of a predetermined thickness to becoextruded around the sheath to form the extrudatc. In this embodimentof the invention, the radiation shield 20 is bolted to die block 129.

One means for effecting the required rapid chilling is illustrated inFIGS. 13 and I4. It provides means for contacting the entire surface ofthe cxtrudate with cooled expanded high-pressure air to give the hotextrudate a smooth surface and to impart to the sheath a radial densitygradient. This chilling means comprises three concentric lengths oftubing, typically about three feet long held in spaced relationship bymeans of annular spacing rings I and 141. The outer tubing I42 has twoair inlet ports I43 and I44 opposite each other and located at about thecenter of its length. These are adapted to receive compressed air fromair inlet lines 2] (FIG. 2). The first inner tubing I45 defines anannular air flow passage 146 with the outer tubing, and it is perforatedto provide a number of fluid ports 147 communicating with the innermostannular passage I48 defined between the first inner tubing 145 and asecond inner tubing 149. The second inner tubing has a number of fluidports 150 positioned to be staggcred from the fluid ports I47. The fluidports I50 are cut at an angle to cause the air entering the chillingzone I5I (defined within the second inner tubing) in the form of amultiplicity of streams directed into the chilling zone toward theoutlet end of the chiller at an acute angle with the extrudate surfaceas indicated by the arrows in FIG. I3. The annular passages I46 and I48are sealed at the ends by the annular spacing rings I40 and I41. Thechiller is conveniently supported by two pairs of legs I52 and I53.

From the chiller 19, the extrudate passes to the cooling means 24 ofextended length, typically about 40 feet, adapted to effect indirectheat exchange with a fluid coolant, such as tap water. As shown in FIG.15, the cooling means comprises two end-sealed lengths of copper tubingI60 and I61 soldered together and having a fillet I62 formed of a goodheat conducting material contoured to contact a part of the surface ofthe extrudate 22. The coolant is delivered to the forward end of each ofthe tubings through inlet conduits 25 and 25a and withdrawn at the afterend through discharge conduits 26 and 26a. Final additional cooling, ifdesired, may be effected by directly contacting the extrudate surfacewith a fluid coolant, e.g.. one or more fine streams of water or air.

It is necessary to exert a pulling force on the extrudate to ensure aneven cross section throughout. This pulling force may be developed by anumber of different types of equipment known in the art, the puller 23shown in FIG. I6 comprising two hard rubber rolls I65 and 166 mounted onshafts 167 and I68. One of the shafts is driven by any suitable meansnot shown. It may be desirable to automatically control the speed of theshaft driving means to control and regulate the extrudate diameter.

The cutter 28 (FIG. 2) may be chosen from commercially availabledevices; and it is preferably one that advances as it cuts the forwardmoving extrudate so that it forms a perfectly square cut. Such cuttersare known.

Completed Article of Manufacture The cut lengths 27 of the extrudate mayhave erasers I attached through metal sleeves or ferrules 176 (FIG. [7)to be formed into pencils. The pencils made by the method and apparatusof this invention are readily sharpenable in a mechanical pencilsharpener as well as with a penknife. The outer surface, whether coatedor not, is smooth and can be printed on using the same techniques whichare presently used for allwood sheathed pencils. The actual sheathstructure of the pencils is unique in that it may be seen in crosssection to be formed of finely sized, closed cells. This structure isillustrated in a diagrammatic, not-to-scale drawing in FIG. 18. Thecells 180 nearer the center are typically about 70 microns in diameter,while those cells I8I around the outer edge are substantially closed ornot greater than about I0 microns in diameter. The larger cells may havediameters up to about I00 microns. The cell diameter gradient decreasesradially outward to furnish a density gradient which increases radiallyoutward. It may be postulated that the denser outer surface I81providing the smooth surface of the extrudate, together with theinternal cell structure, is due to the controlled amount of moisture, tothe use of the metallic soap, and to the rapid chilling of the extrudateas it exits from the die. As shown, the extrudate is provided with theskin coating 132.

It is believed that the advantages and improved results afforded by thesheath composition, method and apparatus for making pencils, and theresultant product of invention will be apparent from the foregoingdetailed description. Various modifications and changes may be madewithout departing from the spirit and scope of the invention as setforth in the following claims.

We claim:

1. A composition for extrusion around a marking core to form asharpenable sheath, the composition consisting essentially of, byweight, approximately 50 to 75% of an extrusion-grade thermoplasticresin binder having a Vicat softening point above about I80F.,approximately 20 to 40% of fibrous tiller particles selected from thegroup consisting of cellulose and leather, the binder/filler ratio beingapproximately L to 3.0, and approximately 0.5 to l5% ofa substantiallywater insoluble metallic soap.

2. A composition according to claim 1 wherein the thermoplastic resinbinder is selected from the group consisting of styrene-acrylonitrileresins, acrylonitrilebutadiene-styrene resin, rubber-modified impactpolystyrene resins, ethyl cellulose, cellulose ester resins,homopolymers and eopolymers of vinyl resins, and mixtures thereof.

3. A composition according to claim 1 wherein the fibrous filler is acomminuted cellulosie material.

4. A composition according to claim 3 wherein the comminuted cellulosicmaterial is wood flour having a particle size approximately 75 to 425microns.

5. A composition according to claim 1 wherein the metallic soap isaluminum stearate in the form of particles at least 95% of which are ofa size no greater than 75 microns.

6. A composition according to claim I having a moisture content ofapproximately 0.3 to 2%.

7. A composition according to claim 1 wherein the thermoplastic resinbinder is selected from the group consisting ofstyrene-acrylonitrile-resins, acrylonitrile butadicne-styrene resins,ruhbermodified impact polystyrene resins, ethyl cellulose, celluloseester resins, ho-

mopolymers and copolymers of vinyl resins, and mixtures thereof in theamount of approximately 65 to wherein the fibrous filler is a comminutedcellulosic material in the amount of approximately 25%; and wherein themetallic soap is present in the amount of approximately 3 to l0%.

8. A composition according to claim 7 wherein the thermoplastic resinbinder is approximately 70% of an acrylonitrile-butadiene-styrene resin;the fibrous filler is wood flour and present in the amount ofapproximately 25%; and wherein the metallic soap is present in theamount of approximately 50%.

9. A composition according to claim 8 having a moisture content ofapproximately 0.3 to l%.

10. A composition according to claim 1 including 0.05 to 2.0% by weightof a blowing agent.

11. A composition according to claim 1 including 0.5 to 5.0% by weightof an additional extrusion aid.

12. A composition according to claim 7 including 0.05 to 2.0% by weightof a blowing agent.

13. A composition according to claim 7 including 0.5 to 5.0% by weightof an additional extrusion aid.

14. A composition according to claim 7 wherein the comminuted cellulosicmaterial is wood flour having a particle size of approximately to 425microns; and wherein the metallic soap is in the form of particles, atleast of which are no greater than 75 microns in diameter.

15. A composition according to claim 12 wherein the comminutedcellulosic material is wood flour having a particle size ofapproximately 75 to 425 microns; and wherein the metallic soap is in theform of particles, at least 95% of which are no greater than 75 micronsin diameter.

16. A composition according to claim l3 wherein the comminutedcellulosie material is wood flour having a particle size ofapproximately 75 to 425 microns; and wherein the metallic soap is in theform of particles, at least 95% of which are no greater than 75 micronsin diameter.

1. A COMPOSITION FOR EXTRUSION AROUND A MARKING CORE TO FORM ASHARPENABLE SHEATH, THE COMPOSITION CONSISTING ESSENTIALLY OF, BYWEIGHT, APPROXIMATELY 50 TO 75% OF AN EXTRUSIONGRADE THERMOPLASTIC RESINBINDER HAVING A VICAT SOFTENING POINT ABOVE ABOUT 180*F., APPROXIMATELY20 TO 40% OF FIBROUS FILLER PARTICLES SELECTED FROM THE GROUP CONSISTINGOF CELLULOSE AND LEATHER, THE BINDER/FILLER RATIO BEING APPROXIMATELY1.5 TO 3.0, AND APPROXIMATELY 0.5 TO 15% OF A SUBSTANTIALLY WATERINSOLUBLE METALLIC SOAP.
 2. A composition according to claim 1 whereinthe thermoplastic resin binder is selected from the group consisting ofstyrene-acrylonitrile resins, acrylonitrile-butadiene-styrene resin,rubber-modified impact polystyrene resins, ethyl cellulose, celluloseester resins, homopolymers and copolymers of vinyl resins, and mixturesthereof.
 3. A composition according to claim 1 wherein the fibrousfiller is a comminuted cellulosic material.
 4. A composition accordingto claim 3 wherein the comminuted cellulosic material is wood flourhaving a particle size approximately 75 to 425 microns.
 5. A compositionaccording to claim 1 wherein the metallic soap is aluminum stearate inthe form of particles at least 95% of which are of a size no greaterthan 75 microns.
 6. A composition according to claim 1 having a moisturecontent of approximately 0.3 to 2%.
 7. A composition according to claim1 wherein the thermoplastic resin binder is selected from the groupconsisting of styrene-acrylonitrile-resins,acrylonitrile-butadiene-styrene resins, rubber-modified impactpolystyrene resins, ethyl cellulose, cellulose ester resins,homopolymers and copolymers of vinyl resins, and mixtures thereof in theamount of approximately 65 to 70%; wherein the fibrous filler is acomminuted cellulosic material in the amount of approximately 25%; andwherein the metallic soap is present in the amount of approximately 3 to10%.
 8. A composition according to claim 7 wherein the thermoplasticresin binder is approximately 70% of an acrylonitrile-butadiene-styreneresin; the fibrous filler is wood flour and present in the amount ofapproximately 25%; and wherein the metallic soap is present in theamount of approximately 50%.
 9. A composition according to claim 8having a moisture content of approximately 0.3 to 1%.
 10. A compositionaccording to claim 1 including 0.05 to 2.0% by weight of a blowingagent.
 11. A composition according to claim 1 including 0.5 to 5.0% byweight of an additional extrusion aid.
 12. A composition according toclaim 7 including 0.05 to 2.0% by weight of a blowing agent.
 13. Acomposition according to claim 7 including 0.5 to 5.0% by weight of anadditional extrusion aid.
 14. A composition according to claim 7 whereinthe comminuted cellulosic material is wood flour having a particle sizeof approximately 75 to 425 microns; and wherein the metallic soap is inthe form of particles, at least 95% of which are no greater than 75microns in diameter.
 15. A composition according to claim 12 wherein thecomminuted cellulosic material is wood flour having a particle size ofapproximately 75 to 425 microns; and wherein the metallic soap is in theform of particles, at least 95% of which are no greater than 75 micronsin diameter.
 16. A composition according to claim 13 wherein thecomminuted cellulosic material is wood flour having a particle size ofapproximately 75 to 425 microns; and wherein the metallic soap is in theform of particles, at leasT 95% of which are no greater than 75 micronsin diameter.